1. Field of the Invention
The invention relates to thermoplastic molding compositions and more particularly relates to compositions of blended aromatic polycarbonate resins and polyamide resins.
2. Brief Description of the Prior Art
Blends of polycarbonate resin and polyamide resin, such as amorphous polyamide, have been found to possess a unique combination of properties which include, for example, high resistance to permeation by gases such as oxygen and carbon dioxide, low water absorption, high creep resistance, and good organic solvent resistance. However, as with other thermoplastic resin blends, it is often desirable to enhance the impact resistance for particular applications. For example, impact modification of amorphous polyamide/polycarbonate blends may be desirable when used to mold liquid containers or exterior automotive parts. It has been suggested to enhance the impact resistance of polyamide/polycarbonate blends through the use of the so-called "super-tough nylons". However, with super-tough nylons, the impact modifier is grafted onto the polyamide, requiring a separare processing step. It is desirable to obtain a compatible impact modifier system which is highly effective and can be introduced to the polyamide/polycarbonate blend without graft processing.
Numerous methods and materials are available for impact modifying each of the polyamides and polycarbonates when separate and unblended. For example; core-shell graft copolymers have been used to impact modify polycarbonates, polyesters and blends thereof, as disclosed in U.S. Pat. Nos. 4,264,487, 4,697,075 and 4,542,179, and ethylene-propylene copolymers have been used to impact modify amorphous polyamides in U.S. Pat. No. 4,536,541. These disclosures are of little assistance in achieving the objects of the present invention since the effectiveness of impact modifiers is not predictable. This is particularly true for binary blends, such as this invention, where each constituent differs from the other in structure, molecular weight, functional groups, polarity, solubility, etc. An impact modifier may be insoluble or unstable in one of the resins causing it to be ineffective or it may cause delamination of the blend where two phases are present. It is desirable to obtain highly effective impact modifiers for polyamide/polycarbonate blends which do not introduce significant deleterious side effects.